If you're CAN-SPAM compliant, showing unsubscribe links, physical address etc, you don't have a policy problem. You have a relevance problem.

Frequency and chasing prospects are not bad, as a matter of fact they can be quite good. But you have to be relevant to what the customer expects to get this to work.

Let me go through a purposefully ridiculous example: let's say I run a pet store that sells dogs, cats and fish.

You're in the market for a puppy. So you click on my facebook ad for the puppy owner manual (or the google ad, or the list drop, or whatever) and enter your email.

You get your puppy email but you also start getting cat and fish emails. 2 out of 3 emails are about litter boxes and aquariums. Worse yet, it's international cat week and I'm hitting you every day with a liquidation sale offer for kittens.

You unsubscribe. And you hit SPAM. Because you never asked for that.

On the other hand, if you happened to get dog emails, you would probably be interested in them and stay on the list. In fact, since you're in the market you would probably take as much as you can get.

Same frequency on the surface, totally different story with relevance.

You don't have to have multiple products to take advantage of this. You always will have multiple customer motivations and often will have separate avatars.

It boils down to marketing strategy and is implemented throughout your customer acquisition process from inbound/outbound lead gen all the way through marketing automation.

The best practice is to never automatically add someone to your email list because they simply contacted you. This is a poor practice. Instead, entice them in the email reply to sign up for the list.

There are 2 levels to this answer:

1. Your technical sending infrastructure. This is a must have to get your emails even just delivered to the mailbox. This includes IP reputation/Senderscore, domain reputation, being on any whitellists or blacklists etc. You need to have this in order not to get blocked.

2. Your engagement metrics. OK your emails are getting delivered but are they making it to the inbox instead of the spam folder? This is about choosing the subject lines, email content, email format, send times and days that generates the most engagement (open rates, mostly). This will help your emails avoid the spam folder which in turn will reduce your likelihood of your emails being blocked in the first place

You can use spam-filters. Barracuda is a commonly used hardware-based gateway spam filter. Examples of cloud-based spam filters include Cloudmark and Symantec. Microsoft SmartScreen, G-Lock SpamCombat are a few examples of desktop-based spam filters that you can use.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath